Virtual eXtensible Local Area Network (VXLAN) is an overlay technology for network virtualization. It provides Layer-2 extension over a Layer-3 underlay infrastructure network by using Media Access Control (MAC) in Internet Protocol/User Datagram Protocol (IP/UDP) tunneling encapsulation. VXLAN tunnel end point (VTEP) is a software or hardware component that performs VXLAN encapsulation and decapsulation. The IP address used by a VTEP as the source address for VXLAN encapsulation is called VTEP address. Multiprotocol Border Gateway Protocol Ethernet Virtual Private Network (MP-BGP EVPN) provides protocol-based VTEP peer discovery and end-host reachability information distribution that allows more scalable VXLAN overlay network designs suitable for private and public clouds.
In EVPN, MAC/IP routes are advertised in Route Type-2 (RT-2) EVPN Network Layer Reachability Information (NLRI), and IP prefix routes are advertised in RT-5 EVPN NLRI. In the BGP update message, the Next Hop (NH) field is the VTEP address. The Router's MAC Extended Community carries the router MAC of the VTEP. The receiving VTEP uses this MAC as the inner destination MAC (DMAC) for routed packets and BGP NH address as VXLAN tunnel destination address.
Virtual Port Channels (vPC) is a type of multi-chassis link aggregation (for EtherChannel) solution that presents two paired devices as a unique Layer 2 logical node to devices connected to them. vPC offers the redundancy protection through dual active/active default gateways for servers.
One software architecture for L2 and L3 VxLAN overlay networks employs an EVPN control plane. A virtual IP address (VIP) shared by both vPC peers is used as the VTEP address for advertising hosts and prefixes learned by the vPC peers. The device router MAC is carried in the Router's MAC extended community. Traffic sent to the virtual IP address will be forwarded to one of the vPC peers based on underlay routing. In a non vPC case, the primary IP (PIP) address of the box is used as the VTEP address. The use of virtual IP as a VTEP address allows the remote end point to view the vPC peers as a logical entity and is essential to MAC address installation, when most vendors do not support MAC level equal-cost multi-path (ECMP). This introduces problems in packet forwarding to prefixes that are known only to one of the vPC peers.